Chromium acid solutions containing hexavalent chromium are used in a number of industrial processes. For example, such processes include chrome plating, copper stripping, aluminum anodizing, corrosion inhibition, photography, purification of oil and acetylene, hardening materials, and as an oxident in organic chemical reactions.
Over time, the chromium solution loses effectiveness in the chemical process because the active hexavalent chromium is chemically converted into the trivalent form. In the past, the solution eventually became ineffective due to the presence of trivalent chromium and was disposed of as waste. This generated a significant environmental problem and cost.
U.S. Pat. No. 4,337,129, issued June 29, 1982 presents a method for the regeneration of spent chromium solution. The method included the presence of a spent chromium solution within an anode compartment, which is separated from a cathode compartment by a cation selective membrane. An electrical potential is created between an anode in the anode compartment and a cathode in the cathode compartment. The current flow between the anode and cathode oxidizes the trivalent chromium to the desired hexavalent form and regenerates the chromium solution in the anode compartment for reuse. Further details of the method are set forth in a United States Department of the Interior, Bureau of Mines Report of Investigations 8377, entitled "Regeneration and Recycling of Waste Chromic Acid-Sulphuric Acid Etchants."
Under a cooperative agreement with the Bureau of Mines, Bell Helicopter Textron, Inc. undertook an application of the basic method disclosed in U.S. Pat. No. 4,337,129. Details and results of that effort are published in a paper entitled "Recovery and Recycling of Chromium-Bearing Solutions" by L. C. George, M. L. Rogers and Glenn L. Horter.
While an effective method thus exists for regeneration of spent chromium solution, a need exists for an effective apparatus or device for efficiently practicing this method.